Lately, it is further severely demanded to reduce a fuel consumption of an automobile in connection with a worldwide effluent control of carbon dioxide associated with a growing interest in environmental problems. In order to cope with such a demand, it is demanded to reduce a rolling resistance as a tire performance. As a means for reducing the rolling resistance of the tire, there has hitherto been examined a method of optimizing the tire structure, but it is most generally attempted to use a rubber composition having a low heat buildup as a rubber composition applied to the tire at the present.
As a means for obtaining such a rubber composition having a low heat buildup, there are considered the decrease in an amount of a filler such as carbon black, silica or the like, the use of carbon black having a large particle size and the like. In any cases, however, there can not be avoided the deterioration of the reinforcing property, wear resistance and grip performance on a wet road surface of the rubber composition.
As another means for obtaining the rubber composition having the low heat buildup, there are developed many techniques of improving the dispersibility of the filler in the rubber composition. Among them is most effective a method wherein a polymerization active site of a conjugated diene-based polymer obtained through an anionic polymerization with an alkyl lithium is modified by a functional group interactive with a filler.
For example, there are known a method wherein carbon black is used as a filler and a modified conjugated diene-based polymer formed by modifying a polymerization active site with a tin compound is used as a rubber component (see JP-B-H05-87530), a method wherein carbon black is used as a filler and a modified conjugated diene-based polymer formed by modifying both polymerization active terminals with a tin compound is used as a rubber component (see JP-A-H06-49279), a method wherein carbon black is used as a filler and a modified conjugated diene-based polymer formed by introducing an amino group into a polymerization active terminal is used (e.g. see JP-A-S62-207342, JP-A-H06-199923, JP-A-H08-231658 and JP-A-H08-225604) and so on.
However, when the modified conjugated diene-based polymer is used as a rubber component, if a large amount of a softening agent, particularly aromatic oil is compounded, the effect of improving the dispersibility of the filler is not sufficiently developed and there is a problem that the workability, low heat buildup, fracture characteristics and wear resistance of the rubber composition cannot be sufficiently improved.